1. Field of the Invention
The invention relates to a driving circuit of a liquid crystal display (LCD) panel and its related driving method, and more particularly, to a driving circuit for applying over two data impulses to a pixel electrode within one frame period, and its related driving method.
2. Description of the Prior Art
A liquid crystal display (LCD) has advantages of lightweight, low power consumption, and low divergence and is applied to various portable equipment such as notebook computers and personal digital assistants (PDAs). In addition, LCD monitors and LCD televisions are gaining in popularity as a substitute for traditional cathode ray tube (CRT) monitors and televisions. However, an LCD does have some disadvantages. Because of the limitations of physical characteristics, the liquid crystal molecules need to be twisted and rearranged when changing input data, which can cause the images to be delayed. For satisfying the rapid switching requirements of multimedia equipment, improving the response speed of liquid crystal is desired.
Generally when driving an LCD, a driving circuit receives a plurality of frame data and then generates corresponding data impulses, scan voltages, and timing signals, according to the frame data, in order to control pixel operation of the LCD. Each of the frame data includes data for refreshing all of the pixels within a frame period; thus each of the frame data can be regarded as including a plurality of pixel data, and each of the pixel data is for defining the gray level that a pixel is required to reach within a frame period. In the general standard, each pixel can switch among 256 (28) gray levels, thus each of the pixel data is 8 bits in length.
Please refer to FIG. 1 showing a timing diagram of pixel data values varying in accordance with the frames. When driving a pixel, the driving circuit receives a plurality of pixel data used for driving the pixel in sequence. As shown in FIG. 1, GN, GN+1, GN+2 are the pixel data received in frame periods N, N+1, N+2, and the driving circuit determines the gray level of the pixel in the frame periods N, N+1, N+2 according to the values of the pixel data GN, GN+1, GN+2. In general, the larger the value of the pixel data is, the larger the gray level is. The driving circuit generates a data impulse corresponding to a frame period according to the pixel data GN, GN+1, GN+2, and applies the pulse to a pixel electrode of the corresponding pixel to have the pixel be in the appropriate gray level as required within each frame period.
Please refer to FIG. 2 showing a timing diagram of different transmission rates of a pixel, varying in accordance with the frames. Two curves C1, C2 are measured when the driving circuit changes the transmission rate from T1 to T2 beginning at frame period N. The curve C1 shows the transmission rate of a pixel not overdriven corresponding to the frames, and the curve C2 shows the transmission rate of the pixel overdriven corresponding to the frames. The U.S. published application No. 2002/0050965 is one of the references of the conventional overdriving method. There is a time delay when charging liquid crystal molecules, so that they cannot twist at a predetermined angle at a predetermined transmission rate. As shown by the curve C1, in the case of not being overdriven, the transmission rate cannot reach a predetermined level in the frame period N but has to wait until the frame period N+2. Such a delay causes blurring. In order to improve that, some conventional LCD are overdriven, which means applying a higher or a lower data impulse to the pixel electrode to accelerate the reaction speed of the liquid crystal molecules, so that the pixel can reach the predetermined gray level in a predetermined frame period. As shown by the curve C2, in the case of being overdriven, although the reaction speed of the liquid crystal molecules is faster than in case of not being overdriven, the transmission rate has to wait until frame period N+1 to reach T2. Thus, the requirement of reaching T2 in the frame period N still remains unsatisfied.